Brass is composed of Copper and Zinc. The zinc will disappear and you'll end up with a fitting looking whole but only 70% there. I actually used a brass barb in my last engine; a Volvo on the raw water side and replaced it every two years (It was above the waterline). Waited almost to long once. and when I removed it I could easily crush it with a vise grips.
Go Slow
Sail Far
Stay Long